Short- and Long-Term Results with an Active-Fixation, Bipolar, Polyurethane-Insulated Atrial Pacing Lead

Since 1989, 136 Medtronic 4058 and 4058M bipolar atrial screw-in leads have been implanted at the Mayo Clinic. Early lead related complications included dislodgment in 4 (2.9%). Over a median follow-up time of 14.4 months (1 day to 3.3 years), there were 11 lead related complications (undersensing, failure to capture, diaphragmatic pacing, and gross lead dislodgment). Chronic complications resulted in reoperations in four patients (2.9%). Of 77 patients in whom pacing thresholds were measured between 2 and 4 months after implantation, 9 (11.7%) and 2 (2.6%) had high pacing thresholds and very high thresholds, respectively. The Kaplan-Meier estimate of the probability of 1-year complication-free lead survival was 93.5%. There were no lead material failures. We conclude that the 4058/4058M lead implanted in the atrial position has favorable acute and chronic performance data, with a tendency toward high pacing thresholds at 3 months. The cause of this phenomenon and its course over time should be further evaluated.     

Comparison of Vitreous Carbon and Elgiloy Transvenous Ventricular Pacing Leads

In a randomized prospective study of 150 patients, we compared two porous-tipped, finned leads, one with a vitreous carbon tip (surface area = 12 mm2) and the other with an Elgiloy tip (surface area = 8 mm2). We assessed the acute and chronic stimulation thresholds and the ease of implantation of the two leads. The acute current thresholds for the vitreous carbon and Elgiloy-tipped leads were 1.7 +/- 0.5 (+/- SD) mA vs. 1.1 +/- 0.4 mA (0.25 ms pulse width), 1.3 +/- 0.5 mA vs. 0.9 +/- 0.3 mA (0.5 ms), and 1.0 +/- 0.3 mA vs. 0.8 +/- 0.3 mA (0.75 ms), respectively (P less than 0.0005). Impedance at implantation was 473 +/- 121 ohms and 716 +/- 285 ohms (P less than 0.0005) for the carbon-tipped and Elgiloy-tipped leads, respectively. The R-wave amplitudes were 10.2 +/- 5.1 volts and 6.8 +/- 3.0 volts, respectively (P less than 0.0005). Both leads were easy to implant and showed low stable chronic thresholds from 3 weeks after implantation, at which time the stimulation threshold was 1.9 +/- 1.0 volts vs. 1.5 +/- 0.6 volts with the implanted voltage-variable generators and 1.8 +/- 0.8 mA vs. 1.6 +/- 0.6 mA with the implanted current-variable generators. Reoperation for displacement was required for two of the 87 (2.3%) carbon-tipped and 2 of the 67 (3.2%) Elgiloy-tipped leads. There was no exit block nor any other lead-related complication. We conclude that both leads have similar and satisfactory performance.     

Implant Experience with Unipolar Polyurethane Pacing Leads

A total of 905 unipolar polyurethane pacing leads have been implanted by the first author's group, between April 1978 and February 1982, with a mean implant time of 1.4 years. Twelve leads were explanled and analyzed. Eleven of the explanled leads exhibited some degree of surface damage or "frosting." Of the 11, five atrial (Medtronic 6991 U) and one ventricular (Medtronic 6971) lead suffered complete insulation failure. One lead was completely free from surface damage, Clinically, insulation failure presented as muscie stimulation and/or battery depletion. Surface damage appears to be due to an environmental stress cracking (ESC) mechanism. ESC requires both a surface active agent from the hostile biological environment, and stress in excess of a threshold value. The minor surface damage or "frosting" of the eleven explanted leads was typically 10 to 15 microns deep on leads implanted about one year, although one device (15 months) had 30 micron cracks. No lead failures in this series were attributed to this shallow cracking mechanism. The severe cracking of the six Medtronic leads leading to insulation failure was thought to be due to the unusually high tensile stresses imposed by manufacturing processes and ligatures. The incidence of failure was 7% (5/74) for the Medtronic 6991 U and 0.2% (1/454) for the Medtronic 6971, Medtronic lead manufacturing processes have been modified to reduce the high residual tensile stresses and a fixation sleeve has been added to reduce ligature stress.     

Laser assistance for extraction of chronically implanted endocardial leads: infectious versus noninfectious indications

BACKGROUND: Powered sheaths, including Excimer laser sheaths, were introduced for the removal of transvenous pacing and defibrillator leads. The purpose of this study was to develop an algorithm to better predict which patients are likely to benefit from these devices. METHODS: We reviewed 283 consecutive patients in whom a total of 500 leads (302 pacing and 198 defibrillator leads) were extracted over a 5-year period at our operative facilities. Laser assist was utilized whenever moderate traction failed. RESULTS: In 128 patients, 203 leads were removed for noninfectious indication. In 155 patients, 297 leads for infectious indications, including sepsis 22% (111), pocket infection 23% (115), and erosion 14% (71). Laser assistance was required for 6%+/- 5% (+/- 95% confidence interval) of septic leads, 51%+/- 7% of leads associated with erosion or pocket infection and 60%+/- 7% of noninfected leads (P = 0.001). Laser assistance was necessary more often for leads implanted >12 months (53%+/- 5%) than 12 months or less (6%+/- 5%) (P = 0.001) and for ventricular (52%+/- 6%) compared to atrial (35%+/- 7%) leads (P = 0.001). CONCLUSIONS: Chronically implanted leads (>12 months), especially noninfected leads and leads associated with erosion or pocket infection, should be referred for extraction with powered sheaths to ensure successful removal. However, leads that are associated with systemic sepsis can generally be removed without powered sheaths.     

Steroid-Tipped Leads Versus Porous Platinum Permanent Pacemaker Leads: A Controlled Study

WISH, M., ET AL.: Steroid-Tipped Leads Versus Porous Platinum Permanent Pacemaker Leads: A Controlled Study. There is little data directly comparing steroid-tipped permanent pacemaker leads to otherwise state-of-the-art porous platinum leads. Eighteen patients receiving unipolar generators capable of low voltage outputs were randomized at the time of implant to receive either steroid-tipped leads or porous platinum leads. All leads were unipolar, tined, passive fixation, and placed in the right ventricular apex or atrial appendage. This study is single center. At implant, threshold pulse width was determined at 3 voltages (2.5, 1.5, and 0.8 V). Follow-up thresholds were determined at weeks 1, 2, 3, and 4, and at 3 and 6 months. There was no difference in implant thresholds or amplitudes for sensing. By 2 weeks postimplant, lower thresholds were noted for the steroid leads, and this discrepancy grew more significant with time. There was no significant postimplant rise in threshold for steroid-tipped leads. At 6 months, the average threshold pulse width for ventricular steroid leads at 0.8 V was 0.3 ± 0.1 msec. In contrast, five patients with standard leads did not capture at maximum pulse width at 0.8 V (p < 0.0001). There was no significant difference in the amplitude of the chronic atrial electrogram. This study shows steroid-tipped leads to offer a significant advantage in reducing thresholds early postimplant and chronically.     

Effect of insulation material in aging pacing leads: comparison of impedance and other electricals: time-dependent pacemaker insulation changes

Background: There has been concern over declining bipolar (BP) impedance (Z) in aging polyurethane (PU) cardiac pacing leads. Subsequently, a prospective study was conducted comparing BP Z, threshold (Th), and R‐wave sensing amplitude of 55D PU‐insulated (Model 4024, Medtronic, Inc., Minneapolis, MN, USA) and silicone‐insulated (Model 5024) leads. Methods: This study was initiated by The Iowa Heart Center. Patients with Model 4024 (N = 162) or 5024 (N = 120) pacing leads with at least 6 years implant time were enrolled and followed for an additional 5 years. Results: There was a significant drop in the mean BP Z for the Model 4024 population, between enrollment (6 years) and the final endpoint (11 years), which was in contrast to the Model 5024 which did not see a significant drop in its mean BP Z for this same period. The trend difference seen in the means between the two models was statistically significant (P < 0.0001). In addition, a statistically significant relationship was found between dropping BP Z and rising Th (P < 0.0001). The analysis showed that if BP Z dropped below 200 ohms, the probability of having a >3X increase over baseline, in Th at 2.5 V, increases from approximately 3–7% to as high as 30%. Conclusions: A significant drop in BP Z observed in the PU‐insulated Model 4024 lead was not present in the silicone‐insulated Model 5024 lead. The statistically significant relationship between dropping BP Z and rising Th helps to understand how to better manage patients with aging leads. (PACE 2012; 35:51–57)     

Chronic Steroid-Eluting Lead Performance: A Comparison of Atrial and Ventricular Pacing

It is generally believed that atrial pacing leads have higher stimulation thresholds and long-term complication rates than ventricular leads, and this is one of the factors limiting the use of dual chamber pacing. A study was undertaken to compare atrial and ventricular bipolar tined steroid-eluting leads in two designs: the Medtronic CapSure SP and the Telectronics Encor Dec. There were 123 pairs of leads: 81 CapSure SP and 42 Encor Dec. Bipolar atrial and ventricular stimulation thresholds, electrograms. and pacing impedance were measured using the Telectronics META DDDR pulse generator immediately postimplantation, and at 1, 3, and 6 months for all leads and at 12, 18, and 24 months for the CapSure SP. The only major lead complication was a 2% atrial lead dislodgment rate. All leads demonstrated low stimulation thresholds, with the CapSure SP leads having lower values than comparable Encor Dec leads. All leads had a mean range of 0.53–0.89 V at all testing periods with P < 0.05 for atrial leads only. There were no differences in electrogram size between manufacturers and no instances of atrial and ventricular undersensing. Pacing impedance was about 100 Ω higher for the Encor Dec leads (P < 0.05, atrial leads only), suggesting that these leads will result in lower pacing energy losses provided the pulse generators are at identical settings. More than 90% of patients could be paced chronically in the atrium and ventricle at 2.5 V, but for chronic 1.6-V pacing, the CapSure SP leads were superior. In conclusion, atrial and ventricular steroid-eluting leads of both manufacturers gave excellent stimulation threshold results allowing low energy dual chamber pacing.     

High impedance low energy pacing leads: long-term results with a very small surface area steroid-eluting lead compared to three conventional electrodes

We evaluated the handling performance at implant, and the long-term atrial and ventricular electrical performance of a new generation using a very small surface area (1.2 mm2) steroid-eluting electrode (Medtronic CapSure Z). We compared the performance of CapSure Z to that of traditional passive fixation leads, with and without steroid elution. The study was conducted during 2 years of follow-up. We studied 188 patients (105 males and 83 females; mean age 71 +/- 7 years). All of the patients were implanted with a dual chamber pacemaker and the same type of lead in both chambers. Forty-one patients received CapSure Z leads, 25 patients received Target Tip leads (8-mm2 surface area; no steroid elution), 63 patients received CapSure leads (8-mm2 surface area; steroid elution), and 59 patients received CapSure SP leads (5.8-mm2 surface area; steroid elution). The four groups were homogeneous in regards to sex, age, cardiac disease, and reason for implant. At follow-up, the CapSure Z lead showed sensing values comparable to the other leads, with lower pacing thresholds and higher pacing impedance in both chambers. We evaluated the mean current drained from the pacemaker by the different types of leads when using safe, low energy output settings. We found that by using CapSure Z leads, the mean current was significantly lower than that of the other types of leads (0.42 microA for CapSure Z ventricular lead vs 0.85 for CapSure SP, 1.42 for CapSure, and 1.54 for Target Tip). Thus, the use of the CapSure Z lead, combined with low energy output programming, will increase pacemaker longevity compared to the use of traditional leads and standard output programming.     

Decrease in Canine Endocardial and Epicardial Electrogram Voltages with Exercise: Implications for Pacemaker Sensing

Individuals with permanently implanted pacemakers who have normal sensing and pacing at rest may demonstrate abnormalities, particularly of atrial sensing, with exercise. Exercise is known to cause changes in the surface electrocardiographic voltages. The purpose of this study was to evaluate changes in endocardial and epicardial voltages during exercise in canines with permanently implanted pacing leads similar to those permanently implanted in humans with pacemakers. Six adult mongrel dogs were equipped with transvenous atrial and ventricular endocardial bipolar screw-in leads from a jugular venosection, and with atrial and ventricular bipolar stab-on leads from a left thoracotomy. Exercise was performed at one week following implantation and at weekly intervals for a total of 4 weeks. The animals were studied at rest and at a single workload of 3 miles per hour at a 30% elevation. Unfiltered electrograms were recorded with a VR-12 Electronics-for-Medicine photographic recorder. The mean decreases of electrograms with exercise from resting voltage were: 15% for atrial endocardial unipolar leads; 11% for atrial endocardial bipolar leads; 4% for atrial epicardial unipolar leads; 15% for atrial epicardial bipolar leads; 8% for ventricular endocardial unipolar leads; 18% for ventricular endocardial bipolar leads; 0.1% for ventricular epicardial unipolar leads and 5% for ventricular epicardial bipolar leads.     

Postpacemaker implant pericarditis: incidence and outcomes with active-fixation leads

Pericarditis has been noted as a potential complication of pacemaker implantation. This study evaluated the risk of developing pericarditis following pacemaker implantation with active-fixation atrial leads. Included were 1,021 consecutive patients (mean age 73.4+/-0.4 years, range 16-101 years; 45.2% women) undergoing new pacemaker system implantation between 1991 and 1999 who were reviewed for the complication of pericarditis. The incidence and outcomes of postimplantation pericarditis in patients receiving active-fixation atrial leads were compared to those not receiving these leads. Of 79 patients who received active-fixation atrial leads, 4 (5%) developed pericarditis postpacemaker implantation. Of 942 patients with passive-fixation atrial leads or no atrial lead (i.e., a ventricular lead only), none developed pericarditis postoperatively (P < 0.001). Of patients receiving active-fixation ventricular leads only (n = 97), none developed pericarditis. No complications were apparent at the time of implantation in patients who developed pericarditis. Pleuritic chest pain developed between 1 and 28 hours postoperatively. Three patients had pericardial rubs without clinical or echocardiographic evidence of tamponade. They were treated conservatively with acetylsalicylic acid or ibuprofen and their symptoms resolved without sequelae in 1-8 days. One patient (without pericardial rub) died due to cardiac tamponade on postoperative day 6. Postmortem examination revealed hemorrhagic pericarditis with no gross evidence of lead perforation. Pericarditis complicates pacemaker implantation in significantly more patients who receive active-fixation atrial leads. It may be precipitated byperforation of the atrial lead screw through the thin atrial wall. Patients developing postoperative pericarditis should befollowed closely due to the risk of cardiac tamponade.     

Chronic Performance of Steroid-Eluting Epicardial Leads in a Growing Pediatric Population:

Patient size and congenital heart defects complicate pacemaker therapy in children favoring an initial epicardial approach. Steroid-eluting (SE) epicardial (EPI) leads maintain stable, low pacing thresholds in the short-term when compared to the nonsteroid (NSE) epicardial (EPI) leads. The purpose of this study was to evaluate chronic, 10-year performance of SE leads in growing children compared with NSE EPI leads implanted during the same time interval. From 1990 to 2000, 35 patients (age 1 month to 18 year, median 3 years), 28 with and 7 without congenital heart disease (CHD) received 51 SE leads: 27 ventricular and 24 atrial. NSE leads were implanted in 27 patients (age 1–28 years, median 8 years), 24 with and 3 without CHD: 27 ventricular and 1 atrial. Pacing lead threshold, impedance, and energy were measured at implant and during a 10-year follow-up. Unpaired t-test showed that impedance remained stable for all leads with lower mean values for the SE   (376 ± 55 vs 443 ± 109 Ω) (P = NS)   . The mean energy requirement for SE leads at 10 years   (1.2 ± 0.9 μJ)   was significantly lower than for NSE   (4.4 ± 5.5 μJ) (P < 0.05)   . At 2.5-V output, chronic thresholds for SE leads did not significantly differ from implant values for atrial (0.08 vs 0.09 ms) or ventricular (0.08 vs 0.08 ms) sites. There were no differences in SE lead performances among patients with or without CHD. Fracture or dislodgement occurred in two SE (4%) and four NSE (14%) leads. SE outperform NSE EPI leads and show stable, chronic low thresholds over time in all growing children. (PACE 2003; 26[Pt. I]:1467–1471)     

Implantation of active fixation leads in coronary veins for left ventricular stimulation: report of five cases

BACKGROUND: Securing transvenous left ventricular (LV) pacing leads without an active fixation mechanism in proximal coronary vein (CV) segments is usually challenging and frequently impossible. We investigated how active fixation leads can be safely implanted in this location, how to avoid perforating the free wall of the CV, and how to recognize and respond to perforations. MATERIALS AND METHODS: In five patients with no alternative to LV pacing from proximal CV segments, 4 Fr SelectSecure (Medtronic, Minneapolis, MN, USA) leads, which have a fixed helix, were implanted through a modified 6 Fr guide catheter with a pre-shaped tip (Launcher, Medtronic). RESULTS: Active fixation leads were successfully implanted in proximal CVs in five patients. There were no complications. Acute and chronic pacing thresholds were comparable to those of conventional CV leads. The pre-shaped guide catheter tip remains in close proximity to the myocardial aspect of the CV, directing the lead helix toward a safe implantation site. CONCLUSIONS: If only proximal CV pacing sites are available, 4 Fr SelectSecure leads can be safely implanted through a modified Launcher guide catheter, avoiding more invasive implantation techniques. Other than venous stenting or implantation of leads with retractable tines, SelectSecure leads are expected to remain extractable.     

Actuarial Survival of Transvenous Pacing Leads in a Pediatric Population

This study was undertaken to examine the actuarial survival of endocardial pacing leads in a pediatric population. We prospectively followed 148 children and young adults age 4 months to 38 years. Of these, 58 had normal cardiac anatomy and 90 had surgically corrected congenitai heart disease. A total of 213 leads were inserted in these patients. Actuarial analysis showed that at 5 years 76.0% of the pacemaker leads were still in use. The reasons for abandonment included death (10), exit block (8), lead fracture (8), adapter malfunction (7), and other including infection, lead migration, and pacemaker malfunction (12). Excluding deaths, an actuarial survival curve was constructed. Stepwise discriminant analysis and independent measures of association showed a significant difference in lead abandonment when the leads placed in the atrium were compared to those placed in the ventricle (30 vs 5: P < 0.0005). Lead insulating material, cardiac anatomy, and/or indication for pacemaker placement had no statistically significant impoct on lead survival.     

Randomized comparison of J-shaped atrial leads with and without active fixation mechanism

BACKGROUND: In this prospective, randomized, controlled study, we compared the performance of J-shaped active fixation (AF) atrial leads with J-shaped passive fixation (PF) leads, over a 1-year follow-up period. METHODS: A total of 200 consecutive patients were prospectively randomized for implantation with a Medtronic 5568 AF lead model (n = 103; Minneapolis, MN, USA) versus a Medtronic 5592 PF model (n = 97), and all lead-related measurements and complications were recorded over one year. RESULTS: All leads were successfully implanted with a nonsignificant difference in crossover rate to the alternative lead due to failed implantation (1 in the AF and 4 in the PF group, P = NS). Fluoroscopy time during implantation procedure was significantly shorter in the PF group (2.1 +/- 3.6 vs 3.3 +/- 4.5 minute, P < 0.05). Pacing thresholds during implantation were significantly lower in patients with PF leads (0.7 +/- 0.3 V vs 0.9 +/- 0.3 V, P < 0.001) and this difference persisted at 1-year follow-up (0.8 +/- 0.6 V vs 1.3 +/- 0.9 V in PF and AF leads respectively, P < 0.05). Lead-related complications occurred in PF and AF with similar frequency (4% and 9% respectively, P = 0.2). However, pericardial complications occurred only in the AF group (6 cases, P = 0.01). Lead dislodgement was observed in only two cases-both in the PF group (P = 0.3). CONCLUSION: Both types of J-shaped atrial leads had reasonable performance. PF leads required shorter fluoroscopy time for implantation, demonstrated a better pacing threshold over a 1-year follow-up period and had no pericardial complications, while AF lead implantation was complicated by pericardial irritation and/or effusion in 6% cases (P = 0.01).     

Comparison of Lead Complications with Polyurethane Tined, Silicone Rubber Tined, and Wedge Tip Leads: Clinical Experience with 822 Ventricular Endocardial Leads

Lead-related complications have been prospectively studied for 602 unipolar tined endocardial ventricular pacemaker leads implanted over a five-year period. No differences were noted in overall complication rates between 238 polyurethane insulated leads (4.2%) and 364 silicone rubber insulated leads (3.6%). Comparing the total series of 602 tined leads to a retrospective survey of 220 wedge tip leads, a marked reduction in dislodgements (0.3% vs. 7.7%, P<0.001) and reoperations (2.0% vs. 15.0%, P<0.001) was found using tined leads. We conclude that tined ventricular leads are far superior to wedge tip leads with respect to lead complications.     

Reduced frequency of retention wire fractures suggests that elective explantation of affected atrial leads is no longer indicated

Since 1994, 611 patients with atrial Accufix leads have been followed. Consideration was given to explanting these leads based on the presence or absence of fractures of the retention wire. All leads were followed according to a protocol proposed by the manufacturer, chiefly by regular 6-month high quality X rays and fluoroscopic evaluation. The impact of various conditions on the incidence of fracture was evaluated, such as the shape and location of the lead, prior open heart surgery, and the implantation route. The only factor related to the frequency of fractures was the shape of the lead, fractures occurring statistically more frequently if the leads were pulled from their normal J shape into an L or straightened configuration. The frequency of fractures has plateaued at 6 through 9 years with no further occurrence of Class III or IV fractures (protrusion of the fractured segment). Altogether there were nine (1.5%) Class III and Class IV fractures at the 9-year follow-up. Actuarial survival, in Class I or II, was 97%. We concluded, that the frequency of retention wire fractures has plateaued. This information coupled with the knowledge that the Accufix lead extraction can be difficult and dangerous, suggests that the remaining leads are best left in place.     

Chronic Ventricular Electrograms: Do Steroid-Eluting Leads differ from Conventional Leads?

SCHUCHERT, A., ET AL.: Chronic Ventricular Electrograms: Do Steroid-Eluting Leads differ from Conventional Leads? The aim of steroid-eluting leads is to reduce chronic pacing thresholds. Whether steroid-eluting leads also modify acute and chronic R wave amplitudes as well as R wave sensing of the pulse generator was investigated in 31 patients with a unipolar ventricular pacemaker. Four different leads were implanted: Two steroid-eluting leads with different electrode surface areas (8 mm² and 5.8 mm²) and two conventional leads (Target Tip, Elgiloy lead). At implantation filtered R wave amplitudes, peak-to-peak values, and slew rates were measured by a pacing system analyzer. One year after implantation R wave amplitudes were directly determined from intracardiac electrograms and compared to the peak-to-peak data at implantation. Additionally, R wave inhibition was evaluated at a sensitivity setting of 5 mV. There were no differences among the four leads in respect to any of the parameters studied at implantation. At follow-up, no differences in R wave amplitudes were found leading to an appropriate sensing in all leads. Steroid-eluting leads did not differ from conventional leads and a smaller electrode surface area of 5.8 mm² had no influence on ventricular electrogram. Together with a pacemaker with an input impedance of 37 kohms R wave sensing was a correct setting of 5 mV.     

Long-Term Functional Integrity of Atrial Leads

The effectiveness and reliability of atrial leads has been questioned. We studied retrospectively, all atrial leads implanted at our center (n = 494; 438 Medtronic Model 6957J, 56 Medtronic Model 4512) over a 5-year period ending December 31, 1987, to determine the frequency of atrial lead failure (pacing, sensing, or both) and the median duration of proper pacing and sensing function for each lead model studied. Eighty-eight percent of the polyurethane atrial leads continued to function satisfactorily at 5 years, results somewhat better than those reported heretofore in the literature, as well as our own past results with a variety of different lead types. There were 29 failures of pacing, sensing, or both (6% of implants). The cumulative survival of the atrial leads at 5 years was 88%. Pacing and sensing survival were 91%± 2.4% and 88%± 2.9%, respectively. We conclude that the choice of pacing mode for a new pacemaker should be based solely on the clinical indication and not on the concern that atrial pacing and sensing will be unreliable.     

Clinical Surveillance of a Tined, Bipolar, J-Shaped, Steroid-Eluting, Silicone-Insulated Atrial Pacing Lead

Since 1990, 558 Medtronic 5524 bipolar, silicone-insulated, J-shaped, tined, steroid-eluting atrial leads have been implanted at the Mayo Clinic (Rochester, MN, USA) and the Midelfort Clinic (Eau Claire, WI, USA). Implantation data were favorable, with pacing thresholds at implantation (median threshold, 0.6 V) better than most published data on other atrial leads. The rate of acute lead-related complications (dislodgment and diaphragmatic pacing) necessitating reoperation or electrical abandonment of the atrial lead was 0.9%. This rate is lower than that in most published series of atrial leads. Over a median follow-up time of 17.5 months (up to 69 months), there were no chronic lead-related complications and no definite or suspected failures of lead material. This rate is much lower than that with other atrial leads studied previously. We conclude that the Medtronic 5524 atrial lead combines the reliability of silicone insulation with a lack of chronic complications and high thresholds due to its steroid elution and with stability in the atrium due to its J shape despite a passive fixation mechanism. There is no evidence of lead material failure during up to 6 years of follow-up.     

Comparison of Unipolar and Bipolar Active Fixation Atrial Pacing Leads

The purpose of this investigation was to compare the acute pacing and sensing characteristics of a new bipolar active fixation atrial pacing lead with those of a unipolar atrial lead of similar design. Pacing threshold voltage and current, lead impedance, and atrial electrogram amplitude and slew rate were measured at the time of surgery in 28 consecutive patients undergoing DDD pacing system implantation. Eleven patients received a Medtronic 6957J-58 unipolar active fixation atrial lead and 17 patients were given a Medtronic 4016-58 bipolar lead. Both leads are polyurethane-insulated with the distal electrode being a platinum alloy screw-helix with a surface area of 8.0 mm2. There were no significant differences in the threshold voltage (1.01 V unipolar versus 1.05 V bipolar) or current (1.93 mA unipolar versus 1.78 mA bipolar) of the two leads. The mean impedance of the bipolar active fixation lead was 618 ohms compared to 479 ohms for the unipolar lead (p = 0.02). The mean amplitude of the atrial electrogram was 4.64 mV for the bipolar lead and 3.11 mV for the unipolar lead (p = 0.02). The atrial electrogram exceeded 5 mV in 10 of 17 patients with the bipolar lead but zero of 11 with the unipolar lead. There was no significant difference in the mean slew rate of the leads (1.09 V/s bipolar versus 0.73 V/s unipolar; p = 0.18). Over a follow-up period of up to 10 months, all patients remained in either the DDD or DDI modes with no episodes of atrial sensing or pacing failure.(ABSTRACT TRUNCATED AT 250 WORDS)